When writing numbers, should we use numerals ("5,000") or words ("five thousand")? I'm particularly interested in how easy each is to read and interpret, and whether it's an important consideration for dyslexic users.
In most cases it's preferable to use numerals. Numerals have a number of advantages that aid readability:
- It's more compact for large numbers (three thousand three hundred and thirty three).
- They stand out among text, which is beneficial because numbers tend to be a key element in a text. I've got ten marbles. I've got 10 marbles. The word ten is as visible as all the other words, but if you go for numerals it's immediately obvious there are 10 of something.
- They can be compared more easily. Three thousand three hundred and thirty three plus one is three thousand three hundred and thirty four. 3333 plus 1 is 3334. This is in line with my first point but also works for small numbers.
- We're so used to numerals, reading and counting with numbers, most people will have to translate the words to numerals in their mind to be able to parse their meaning.
- All this together makes me think numbers should be preferable for dyslexics as well. Having to deal with less text and having a much smaller and simpler string to parse should probably help them deal with numbers*.
*I had a short look for some data on how reading numbers is affected by dyslexia. Obviously there is a big chance you're going to have issues with numbers in terms of sequencing and associating meaning to symbols. See also the International Dyslexia Association on the impact on math. But it doesn't seem to always be the case. In fact, apparently we process text and Arabic numerals using mostly different and separate pathways in our brain (studies from Oxford Journals and Taylor&Francis). This would suggest that if your dyslexia affects the reading of Arabic numerals, having to deal with the simpler shorter strings of the numerals would still be preferable over numbers in words. But there is a chance that some people with dyslexia will be able to deal with Arabic numerals much easier than words.
Personally, I find numerals easier to read, especially when there are many numbers being displayed at once. If the numbers are in a table or other context where they could be compared to other numbers, numerals are the only appropriate choice. When the number appears in a block of text, however, it can be spelled out or represented with numerals.
A common stylistic practice for displaying numbers within text is to spell out smaller numbers, eg, zero through twenty, while using numerals for larger numbers that have longer or hyphenated spellings, eg, twenty-one.
Another consideration is whether the numbers are approximate or exact. I might say ten or twenty but finally settle on 17. It is probably best though not to mix representations within the same sentence.
There are multiple ways of writing numerals
- If you want to draw the user's attention then it's better to use number then in words (eg. use "23" than "twenty-three")
- If you think the exact number is important then show the number, disclosing the exact number (eg. 5042) increases the statement’s credibility.
- If the number is a big number (eg. 2,000,000), it's ideal to user numerals for the significant digits and write out the magnitude as a word. (eg. 20 billion)
The AP Stylebook provides guidelines widely used across the world of journalism. Academic scholarship in the liberal arts (like English Literary Criticism) follows guidelines laid out by the MLA Handbook.
A quick reference to AP Style is published online by many universities, including this one hosted by Purdue:
"For ordinal numbers, spell out first through ninth and use figures for 10th and above when describing order in time or location. Examples: second base, 10th in a row. Some ordinal numbers, such as those indicating political or geographic order, should use figures in all cases. Examples: 3rd District Court, 9th ward.
For cardinal numbers, consult individual entries in the Associated Press Stylebook. If no usage is specified, spell out numbers below 10 and use figures for numbers 10 and above. Example: The man had five children and 11 grandchildren.
When referring to money, use numerals. For cents or amounts of $1 million or more, spell the words cents, million, billion, trillion etc. Examples: $26.52, $100,200, $8 million, 6 cents."